Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $209.94   6.712%   $224.0312   $224.03   $224.05   $224.00  
  Purchase #2 $232.53   13.537%   $264.0076   $264.01   $264.00   $264.00  
  Purchase #3 $15.95   13.423%   $18.091   $18.09   $18.10   $18.10  
  Purchase #4 $177.86   6.489%   $189.4013   $189.40   $189.40   $189.40  
  Purchase #5 $245.71   13.165%   $278.0577   $278.06   $278.05   $278.10  
  Purchase #6 $113.62   8.642%   $123.439   $123.44   $123.45   $123.40  
  Purchase #7 $120.73   10.682%   $133.6264   $133.63   $133.65   $133.60  
  7 purchase totals = $1,116.34       $1,230.6542   $1,230.66   $1,230.70   $1,230.60